The technical field of this invention is automatic speed control for an automotive vehicle.
Automatic speed controls for automotive vehicles are being proposed that extend the range of control past the mere maintenance of a preset highway cruising speed. Some such controls are being designed to control vehicle deceleration to a full stop. But a problem that such controls must surmount is that of increasing noise in the vehicle deceleration signal as vehicle speed decreases. This is due to the facts that (1) vehicle deceleration is generally obtained by differentiating a vehicle speed signal and (2) most practical vehicle speed sensors depend on pulse generation by rotating wheels or drive-line components. The time between the generation of successive pulses increases non-linearly as rotational speed decreases and permits an increase in the signal to noise ratio of the vehicle speed signal, which is accentuated in the vehicle deceleration signal.
This invention is a deceleration control for automotive vehicle speed control apparatus that generates an actual vehicle deceleration rate signal, provides a desired vehicle deceleration rate signal and determines vehicle speed. It includes a first memory storing values of a closed loop deceleration command as a function of the desired vehicle deceleration rate signal and a second memory storing values of an open loop deceleration command as a function of the desired vehicle deceleration signal. It further includes a control that provides a braking command to a vehicle braking system during commanded vehicle deceleration. When the determined vehicle speed exceeds a transition threshold value, the vehicle braking command comprises a closed loop vehicle brake command derived from values of the closed loop deceleration command in the first memory. Alternatively, when the determined vehicle speed does not exceed the transition threshold value, the vehicle braking command comprises an open loop brake command signal derived from values of the open loop deceleration command in the second memory.
While the determined vehicle speed exceeds the transition threshold value, the control updates selected values the first memory means to reduce an error between the actual vehicle deceleration signal and the desired vehicle deceleration signal and further preferably updates selected values in the second memory means to reduce an error between the open loop brake command signal and the closed loop brake command signal. The selected values in the second memory means are updated with a gain factor greater than that used in updating the selected values in the first memory means, so that the selected values in the second memory means conform to those in the first memory means. Thus, automatic open loop operation is provided at low vehicle speeds where vehicle deceleration signals are noisy; and a smooth transition is provided between closed loop and open loop operation as the vehicle decelerates.